Cellular communication systems continue to grow in popularity and have become an integral part of both personal and business communications. Cellular telephones allow users to place and receive phone calls almost anywhere they travel. Moreover, as cellular telephone technology is improved, so too has the functionality of cellular devices. For example, many cellular devices now incorporate Personal Digital Assistant (PDA) features such as calendars, address books, task lists, calculators, memo and writing programs, etc. These multi-function devices usually allow users to wirelessly send and receive electronic mail (email) messages and access the Internet via a cellular network and/or a wireless local area network (WLAN), for example.
As the functionality of cellular devices continues to increase, so too does demand for smaller devices that are easier and more convenient for users to carry. Nevertheless, the move towards multi-functional devices makes miniaturization more difficult as the requisite number of installed components increases. Indeed, the typical cellular device may include several antennas, for example, a cellular antenna, a global positioning system antenna, and a WiFi IEEE 802.11g antenna. These antennas may comprise external antennas and internal antennas.
Generally speaking, internal antennas allow cellular devices to have a smaller footprint. Moreover, they are also preferred over external antennas for mechanical and ergonomic reasons. Internal antennas are also protected by the cellular device's housing and therefore tend to be more durable than external antennas. External antennas may be cumbersome and may make the cellular device difficult to use, particularly in limited-space environments. Yet, one potential drawback of typical internal antennas is that they are in relatively close proximity to the user's head when the cellular device is in use, thereby increasing the specific absorption rate (SAR). Also, other components within the cellular device may cause interference with the internal antenna.